The pedal-assisted bikes are bikes equipped with an auxiliary electric motor having the following characteristics:                maximum continuous rated power of the electric motor: 0.25 kW;        motor power supply is gradually reduced and then interrupted when reaching 25 km/h;        motor power supply interrupted before 25 km/h if the cyclist stops pedaling.        
The electric motor is controlled by means of a processing and control unit that manages the power delivery thereof according to the user's pedaling, balancing the insertion of the propulsion in a progressive manner starting from the very beginning of pedaling, so as to make this fluid and regular.
For this purpose, the pedal-assisted bikes are equipped with a torque sensor arranged in correspondence of the pedals or with a speed sensor located in the pedal crank, or both.
In traditional pedal-assisted bikes the electric motor is housed directly in the motorized wheel hub and is powered by a battery pack which, on the contrary, is mounted on the bike frame.
Taking into account the need to equip the bike with all the above components designed for the performance of various functions, the traditional pedal-assisted systems are usually conceived, since their design phase, to be installed on a specific model of bike.
Only rarely, in fact, it is possible to develop kits able to adapt to several models of bike taking into account the considerable diversity among the bikes on the market, in particular their frames which, of course, have so different shapes and sizes to prevent a practical and comprehensive standardization of the pedal-assisted systems.
Furthermore it should be emphasized that the application of a kit for pedal-assisted bikes in a post-sales stage, even if possible, usually needs to perform inconvenient and impractical operations for adjusting and fixing the various components to the frame, which most of the times can not be accomplished by the end user and require the intervention of an expert technician.
To overcome at least in part the above mentioned drawbacks it is known to integrate into the motorized wheel not only the electric drive motor but also the battery pack, the torque sensor and the gear set.
An example of a wheel with these characteristics is illustrated in the patent document WO 2012/123802.
In this wheel the torque sensor consists of a first plate and a second plate revolving around the rotation axis of the wheel.
The second plate, besides revolving around the rotation axis of the wheel, is also axially sliding in the direction of moving away and close with respect to the first plate in contrast to a spring.
The first plate receives the rotational motion produced during pedaling and transmits it to the second plate through a series of rollers that engage the same number of grip ramps on the second plate.
The rotational motion is transmitted from the first plate to the second plate when the rollers and the relative grip ramps reach a specific relative position that allows to transfer to the wheel the torque required by the load conditions during pedaling.
In fact, under low load conditions (e.g. pedaling on flat ground), the rollers are able to transfer motion and drag in rotation the grip ramps and the second plate without any particular difficulties.
Under higher load conditions (e.g. pedaling uphill), on the contrary, the first plate is not able to immediately grip the second plate.
The first plate, therefore, turns idle with respect to the second plate by a certain angle of rotation, which determines the engagement of the grip ramps by the rollers and the sliding of the second plate in contrast to the spring.
This sliding is interrupted at the time when the rollers are able to transmit to the grip ramps a sufficient torque to drag them in rotation and, with them, also the second plate so as to allow the rolling of the wheel.
Similarly, it should be underlined that during pedaling, the user applies a thrust to the pedal crank which has an uneven pattern, characterized by the alternation of continuous maximum and minimum values.
In correspondence of the thrust maximum values, an excessive torque reaches the first plate compared to that required to drag the second plate, and this determines the rise of the rollers on the grip ramps.
In correspondence of the thrust minimum values, on the other hand, the torque reaching the first plate is less and the rollers engage the grip ramps in a different position.
Depending on the transmitted torque, therefore, the rollers take a different position on the grip ramps, resulting in a corresponding distancing of the second plate with respect to the first plate that can be measured by a distance sensor.
The wheel shown in WO 2012/123802, however, is susceptible of upgrading aimed at improving the user's driving comfort and the system's efficiency.
During the thrust phase of pedaling, in fact, the presence of grip ramps delays the transmission of torque from the pedal crank to the wheel.
During the resting phase of pedaling, on the other hand, the return of the spring to the initial position determines a slight reaction force that is discharged on the pedals.
Under both conditions, this behavior of the wheel is felt by the user as annoying and as an obstacle to pedaling.